1. Field of the Invention
The present invention relates to a semiconductor apparatus having a signal line to transmit a signal on at least a substrate and, more particularly, to a semiconductor apparatus which can accurately transmit or process the signal even when the signal level falls in a very small range.
The semiconductor apparatus according to the invention is generally applied to apparatuses for transmitting or processing a signal of a very small level. For example, it is applied to an apparatus for processing a micro photo-current as an output of a photovoltaic device, or the like.
2. Related Background Art
In general, in the case of transmitting and processing a signal having a level in a very small range through a line, it is difficult or impossible to accurately transmit and process the signal because of leakage current from the line or a current flowing into the line from the outside
For example, when the illumination is small and a photovoltaic current of a photodiode is very small, a variation occurs due to leakage current or the like in the output voltage which is derived by amplifying the output of the photodiode by a log amplifier, so that the accurate photoelectric converted output cannot be obtained (refer to FIG. 1). Therefore, hitherto, the signal has been adjusted by use of a correcting circuit which is additionally provided.
However, when the output voltage varies as shown in a hatched portion in FIG. 1, the fine correction becomes difficult and there is such a problem that the signal cannot be accurately processed. Further, particularly, in the apparatus having such a constitution as to receive a number of micro-level signals, the addition of the correcting circuit causes the circuit to be complicated and there are such problems that the manufacturing steps also become complicated in association with the complicated circuit and the manufacturing cost also increases.